With such spectacle lenses and display devices the difficulty arises that the image guided in the spectacle lens by reflection (e.g. total reflection) or the corresponding light wave is influenced e.g. by the curved surface radii, with the result that after each reflection there is a different state of the propagating wave. In particular in the case of guiding by means of total reflection, due to the oblique incidence on the curved surfaces (front and rear sides) which is necessary for the total reflection, errors such as astigmatism and coma occur. It makes no difference whether or not the light was collimated before entering the spectacle lens.
In addition, the fundamental difficulty arises that the diameter of the light bundle guided through the spectacle lens increases, viewed in the direction from the coupling-out section towards the coupling-in section, with the result that only a limited étendue can be guided shading free through the spectacle lens and thus undesired vignetting can occur.
In order to avoid this vignetting, the coupling-out section could be formed with a relatively strong positive refractive power, wherein the thereby altered total focal length, which is predetermined by an image-generating module of the display device, is then to be corrected by means of an adaptation of the refractive power of the coupling-in section. However this leads to very strained optical conditions. In particular, focussed bundles are guided by the curved spectacle surfaces several times during the total reflection at very large angles of incidence due to the shorter focal length of the coupling-out section, whereby image errors such as astigmatism and coma are generated and the overall imaging performance suffers greatly.